Hach-Lange DR 5000 brewerie analysis, supplementary software LZV570 - Manual (Page 40)

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Working procedures
6. Separate the phases and break the emulsion by centrifuging for
5 min at 3000 rpm.
7. Use a pipette to draw off and discard the bottom aqueous
phase. Add sodium sulphate to the iso-octane phase until the
phase clarifies after being shaken vigorously for a short time.
8. Pipette 10 ml of the iso-octane phase into a 25 ml mixing
cylinder.
9. Add 10 ml acidic methanol solution, and mix the contents of the
cylinder by inverting it 100 times
10. Pipette 5 ml of the supernatant clear iso-octane phase into a 25
ml measuring flask.
11. Make up to the mark with alkaline methanol solution and mix.
12. Measure the absorbance of the iso-octane solution at 255 nm
and 360 nm against a blank value solution.
13. Preparation of the blank value solution
a. Pipette 5 ml iso-octane into a 25 ml measuring flask.
b. Fill up to the mark with alkaline methanol solution and mix.
Results
The result is expressed in mg/l without any decimal places
Accuracy
Vcr = ± 5%
Standard values
Beer: 10–40 mg/l iso-
α-acids, depending on type and origin
(< 2mg/l a-acids)
Wort: 15–50 mg/l iso- α-acids, depending on the beer and the level
of bitter substance utilisation
1–15 mg/l a-acid depending on degree of isomerisation
Literature
MEBAK Brautechnische Analysenmethoden
4th Edition 2002 Volume II, pp 116ff